Conventionally, frozen aerated products such as ice cream are manufactured by methods which comprise mixing the ingredients, homogenizing, pasteurizing, freezing, forming/filling, and hardening the frozen mixture. Aeration of the mixture or expansion is carried out at the freezing stage, the proportion of air used being such that the volume increases by 10 to 120%. On leaving the freezer, the temperature of the aerated mass is typically about -5.degree. to -6.degree. C. This is then hardened to -40.degree. to -45.degree. C. in a hardening chamber until the core temperature of the product reaches -18.degree. C. or less for bulk products, or -30.degree. C. for extruded products in bars.
Attempts have been made to lower the temperature of the aerated mass leaving the freezer to below -6.degree. C., both for energy savings and with the aim of improving the texture, for example to obtain greater smoothness. However, with conventional equipment, insurmountable problems of high viscosity of the mass of ice cream at temperatures below -7.degree. to -8.degree. C. are encountered. These problems have been partly resolved by using two scraped surface freezers in series, the first, which is conventional, delivering aerated ice cream at about -7.degree. C., and the second being specifically designed to process the highly viscous mass to lower its temperature to about -10.degree. C. However, it would be desirable to obtain an even lower temperature of the aerated mass and the present invention attempts to make this possible.